compute temp/eff command

Syntax

Examples

compute1alltemp/effcomputemyTempmobiletemp/eff

Description

Define a computation that calculates the temperature of a group of
nuclei and electrons in the electron force field
model. A compute of this style can be used by commands that compute a
temperature, e.g. thermo_modify, fix npt/eff, etc.

The temperature is calculated by the formula KE = dim/2 N k T, where
KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2 for
nuclei and sum of 1/2 (m v^2 + 3/4 m s^2) for electrons, where s
includes the radial electron velocity contributions), dim = 2 or 3 =
dimensionality of the simulation, N = number of atoms (only total
number of nuclei in the eFF (see the pair_eff
command) in the group, k = Boltzmann constant, and T = temperature.
This expression is summed over all nuclear and electronic degrees of
freedom, essentially by setting the kinetic contribution to the heat
capacity to 3/2k (where only nuclei contribute). This subtlety is
valid for temperatures well below the Fermi temperature, which for
densities two to five times the density of liquid H2 ranges from
86,000 to 170,000 K.

Note

For eFF models, in order to override the default temperature
reported by LAMMPS in the thermodynamic quantities reported via the
thermo command, the user should apply a
thermo_modify command, as shown in the following
example:

A 6-component kinetic energy tensor is also calculated by this compute
for use in the computation of a pressure tensor. The formula for the
components of the tensor is the same as the above formula, except that
v^2 is replaced by vx * vy for the xy component, etc. For the eFF,
again, the radial electronic velocities are also considered.

The number of atoms contributing to the temperature is assumed to be
constant for the duration of the run; use the dynamic option of the
compute_modify command if this is not the case.

This compute subtracts out degrees-of-freedom due to fixes that
constrain molecular motion, such as fix shake and
fix rigid. This means the temperature of groups of
atoms that include these constraints will be computed correctly. If
needed, the subtracted degrees-of-freedom can be altered using the
extra option of the compute_modify command.

See this howto section of the manual for
a discussion of different ways to compute temperature and perform
thermostatting.

Output info:

The scalar value calculated by this compute is “intensive”, meaning it
is independent of the number of atoms in the simulation. The vector
values are “extensive”, meaning they scale with the number of atoms in
the simulation.

Restrictions

This compute is part of the USER-EFF package. It is only enabled if
LAMMPS was built with that package. See the Making LAMMPS section for more info.